linux-kernel - Re: [PATCH] perf: Ignore format attributes with an unknown perf_event

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Date:   Thu, 01 Sep 2022 16:22:06 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Rob Herring <robh@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>
CC:     James Clark <james.clark@....com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: Ignore format attributes with an unknown perf_event_attr field



On September 1, 2022 3:47:10 PM GMT-03:00, Rob Herring <robh@...nel.org> wrote:
>If the kernel exposes a new perf_event_attr field in a format attr, perf
>will return an error stating the specified PMU can't be found. For
>example, a format attr with 'config3:0-63' causes an error if config3 is
>unknown to perf. This causes a compatibility issue between a newer
>kernel and an older perf tool.
>
>The addition here makes any attr string up to the ':' ignored, but
>still checks the 'bits' portion.

So, can you please show what is the behavior of the tool, with an actual command line and it's output, before and after your patch?

- Arnaldo

>
>Signed-off-by: Rob Herring <robh@...nel.org>
>---
>This is the YACC mud I threw and seems to stick. Maybe there's a better 
>way to handle this. It doesn't seem like there's a way to do wildcards 
>(i.e. config.*) in YACC.
>
>This is needed for this series[1]. Unfortunately the best we do to avoid 
>the issue is applying this to stable. I think there's some time before 
>v8.7 h/w is deployed, too.
>
>Rob
>
>[1] https://lore.kernel.org/all/20220825-arm-spe-v8-7-v1-0-c75b8d92e692@kernel.org/
>
> tools/perf/util/pmu.y | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/tools/perf/util/pmu.y b/tools/perf/util/pmu.y
>index bfd7e8509869..3096864ec9b9 100644
>--- a/tools/perf/util/pmu.y
>+++ b/tools/perf/util/pmu.y
>@@ -60,6 +60,9 @@ PP_CONFIG2 ':' bits
> 				      PERF_PMU_FORMAT_VALUE_CONFIG2,
> 				      $3));
> }
>+|
>+error ':' bits
>+{}
> 
> bits:
> bits ',' bit_term